JERUSALEM, Dec 20 (Reuters) - A U.S. cable leaked on Monday said Israel and President Mahmoud Abbas's forces worked closely together against Hamas as it took over Gaza in 2007, a potentially embarrassing revelation for the Palestinian leader.

Israel has acknowledged working with Palestinian Authority (PA) security forces loyal to the Western-backed Abbas, but the diplomatic memo leaked by WikiLeaks describes a level of cooperation that could fuel criticism of Abbas by his Islamist rivals.

The 2007 cable quoted Yuval Diskin, the head of Israel's Shin Bet internal security service, as saying the PA security apparatus shares with Israel almost all the intelligence that it collects.

They understand that Israel's security is central to their survival in the struggle with Hamas in the West Bank, the cable said.

The cable, dated June 13, 2007, was sent from the U.S. embassy in Tel Aviv as Hamas forces were routing Abbas's security forces to take over the Gaza Strip. Abbas has since ruled only in the Israeli-occupied West Bank.

Diskin is quoted as calling Abbas' forces in Gaza as desperate, disorganized, and demoralized.

They are approaching a zero-sum situation, and yet they ask us to attack Hamas. This is a new development. We have never seen this before. They are desperate, Diskin said.

A Palestinian official, speaking on condition of anonymity, said the comments were based on an assessment and evaluation rather than solid information.

Hamas has accused Abbas, who has held numerous rounds of peace negotiations with Israel, of plotting with Israel against it. Hamas is sworn to Israel's destruction. (Additional reporting by Mohammed Assadi, Writing by Ari Rabinovitch, Editing by Angus MacSwan)